In civil engineering generally and in land, maritime and offshore constructions, there is widespread use of foundation piles. The piles support the load of a structure to be built in terrains where the ground or subsurface are not sufficiently resistant to loading and may tend to displace under the weight of the structure and with time.
Foundation piles of the type with which the invention is concerned can be made of various materials, but generally are composed of metal and are of a strength sufficient to enable the pile to be driven into the soil by the pile driver.
During the pile-driving operation, the pile being driven into the soil separates the soil outside of the pile from soil contained within the pile and often referred to as the core.
The load carrying capacity of the pile is usually determined by the sum of the friction of its external and internal surfaces with the soil.
In some cases and under some ground conditions, the load capacity provided solely by such friction has been found to be insufficient. It can be increased either by increasing the length of the pile driven into the soil with a higher consumption of piling and more labor for pile driving, thereby increasing the cost of the foundation. It can also be increased by inserting plugs within the piles to prevent the sliding of the soil past the plug. In such cases, the load support capacity is determined in part by the force with which the plugs can react against the soil therebelow.
Various approaches to the plugging of a tubular pile have been used in practice. For example, plugs made of concrete can be used, the concrete being cast in place within the pile after the pile has been driven into the soil. This system has the disadvantage that one must wait for the cast plug to set. Moreover, because the cast plug is somewhat brittle and has only limited compressive strength, it is not possible, in practice, to drive the pile further after the plug has been provided.
It has also been proposed to weld diaphragms within the pile in order to obstruct the cross section thereof. This approach, however, requires determination of the location of the diaphragm with great precision and possibly limit the length of the pile and the manner in which the pile is driven into the soil.
There have also been provided plugs which can be lowered into the pile shortly before a driving operation is completed and which are permanently deformed at the desired location by an internal pressure with the pile being then subjected to addition driving to block the internal core against that plug. While these plugs tend to be highly effective for the purposes described, the plug structures used in the past have required very high forces and pressures to set them into position, thereby making use of such plugs expensive and complex.